Is silk really the strongest substance known?

[Stylesjl]

Pravin Lal says that Spider Silk has the highest tensile strength of any substabce we know of. Is that actually true? Or is it just BS?

 

[TROOPERBLUE]

Personally, I think that Lal is living in a Dream World! He likes to use his imagination alot. And he is happy through his inefficiency. Spider Silk is just one example of this. Hope this helps.

 

[CanseiDeSerSexy]

It's true! Spider silk has slightly less tensile strength than high-tensile steel, but it is way less dense, which means it takes more energy to break it. (I think)

It's definitely really strong at any rate, but its very hard to take advantage of that

 

[Elu Venius]

Spider silk is a fibre secreted by spiders. Spider silk is a remarkably strong material. Its tensile strength is comparable to that of high-grade steel — according to Nature, spider silk has a tensile strength of roughly 1.3 GPa, while one source [1] lists a tensile strength for one form of steel at 1.65 GPa.
However, spider silk is much less dense than steel; its ratio of tensile strength to density is perhaps 5 times better than steel — as strong as Aramid filaments, such as Twaron or Kevlar.
In fact, a strand of spider silk long enough to circle the earth would weigh less than 16 ounces (less than 460 grams).

 

[Disgustipated]

hmm, I couldn't find silk on the wiki article.

http://en.wikipedia.org/wiki/Tensile_strength

But always figured it was carbon nanotubes.

Note: Multiwalled carbon nanotubes have the highest tensile strength of any material yet measured, with labs producing them at a tensile strength of 63 GPa, still well below their theoretical limit of 300 GPa. However as of 2004, no macroscopic object constructed of carbon nanotubes has had a tensile strength remotely approaching this figure, or substantially exceeding that of high-strength materials like Kevlar.

edit: oh, I missed spider silk. It is in there. Doesn't appear to be the highest.

 

[Crimson Sunrise]

I seem to recall (and I haven't gone to materials science classes for years, partly because I graduated) that silk has a frighteningly high strength proportional to its density and the usual size of the strands.

 

[ijuinkun]

IIRC carbon nanotubes DO have a higher strength-to-weight and strength-to-bulk ratio than silk, but so far we have not been able to mass produce unbroken tubes of sufficient length to use as fiber. As for silk, spider silk is stronger than silkworm silk, but MUCH harder to extract in quantity, since spiders do not spin coccoons.

 

[Vatras]

Lal is right at the moment, but from a fiber of high strength to a useable product is a really long way to go, and in some cases, may never be done

Technically it is possible to make ropes of spider silk, but the process is somewhat akin to getting the gold out of seawater...also possible, but it costs a lot more to get it out than the gold is worth...

 

[Cuivienen]

edit: oh, I missed spider silk. It is in there. Doesn't appear to be the highest.

But Lal never says that it is currently the highest, only that it was the highest for many centuries (which is certainly true; carbon nanotubes and high-tensile steel are recent innovations).

 

[zomglazorgunpew]

Ooh, I wrote a paper on the scientific progress chemists are making with "Silksteel".

Anyways, yeah, silk is (off my head) 100 times stronger than steel, and more flexible than rubber. If it can be produced in large quantities, it really could be put to amazing uses.

 

[BananaLee]

It all depends on your definition of "strength" as many people (non-engineers) mistake the difference between toughness and strength.

Strength is the capability of a material to withstand stresses, usually described in most materials as "yield stress" (stress at which the material undergoes plastic deformation) or "ultimate tensile strength" (stress at which the atoms of a material separate).

Toughness, on the other hand is a measure of how much energy a material can absorb prior to breaking.

Therefore, a piece of chalk has relatively high strength and low toughness, while a lump of Blu-tac has high toughness but low strength.

Regarding silk, a quick University database search has given me an interesting article and here's a direct quote (italics added by me for emphasis): -

Although the tensile strength of MA spider silks is similar to other polymeric biomaterials such as cellulose, collagen and chitin, their extensibility is considerably greater. Thus, their toughness or the energy required to break spider silk can be 10 times greater than these other biological materials.
It is fair to say that spider MA silk is among the stiffest and strongest polymeric biomaterials known.
However, the stiffness of MA silk is well below that of Kevlar, carbon fiber and high-tensile steel, engineering materials that are commonly employed to transmit and support tensile forces. Note also that the strength of MA silk is somewhat less than that of these engineered materials. In spite of its somewhat inferior strength, the large extensibility of MA silk makes it tougher than the engineering materials.

*Own Note: Stiffness (E) is a function of strain and stress - a high stiffness does not necessarily mean high strength, compare chalk and a plastic tube - both have similar stiffness but different strengths